Computer software may be purchased in various forms, such as on a computer readable medium. A user may then install the software on his/her computer system. The same purchased copy of software may be easily replicated and also installed on multiple machines. The software product vendor may want to control use of each purchased copy of the software product in accordance with the scope of the user's license such as, for example, not allow use of a same purchased copy on more than one computer system. In order to control use of purchased copies of the software product in accordance with a purchaser's license terms, different techniques may be utilized. One existing technique includes requiring activation of the software product after installation in order to use the installed software. For activation purposes, a product key consisting of letters and/or numbers may be included with each purchaser's copy of the software product. A different product key may be included with each purchaser's copy of the software product. After the software is installed on a computer by a user, a hardware identifier is generated. The hardware identifier may be characterized as a “fingerprint” of the user's computer on which the software has been installed. The hardware identifier may be produced using multiple hardware attributes of the user's computer. As part of the activation process, the user registers the hardware identifier with the product key. The hardware identifier is associated with the product key and may be used to track and control subsequent activations of the same purchased copy. For example, a same purchased copy of software may be installed on two computer systems each having a different hardware identifier. Activation may be completed for a first of the computer systems having a first hardware identifier. The user may attempt to activate the software for use on the second computer system. If the license terms only allow the purchased copy of the software to be activated on a single computer system, the activation process for the second computer may fail. As part of activating the software on the second computer, it is determined that the software having the product key is already activated on the first computer having the first hardware identifier.